In certain circumstances, it is desirable to inject medicament directly into human tissue. In the contemporary art, a user draws liquid medicament from a vial using a syringe needle and then injects the medicament into a tissue layer using the same syringe needle. The contemporary art requires that the user have access to a vial and a separate syringe each time an injection is necessary.
Accordingly, the user must carry the vial and one or more syringes on his or her person at all times. Moreover, the user must repeat the tiresome process of drawing the desired medicament dose from the vial with a syringe needle and then injecting the medicament into a tissue layer using the same syringe needle each time an injection is required.
Alternatively, a user may attach a pen needle to a pen injection device to enable injection. This may be viewed as a more convenient form of human tissue injection since a medicament and dose metering are integrated into the pen. Pen injection devices generally have the added convenience of space and ease of usage and transportation, and pen needles are widely available in standard and interchangeable designs.
Pen injection devices, however, present a challenge of high thumb pressure when injecting viscous formulations, or while using small gauge needles. Additionally, the combination of pen needles and pen injection devices may not be suitable for intradermal injections due to the backpressure that the fluid needs to exceed for injection to occur.
Typically, self-injectors inject liquid medicaments into tissue areas, such as the intramuscular tissue layer, the subcutaneous tissue layer, or the intradermal tissue layer. Each of these tissue layers has specific characteristics that affect the amount of fluid pressure needed to inject a fluid into the targeted tissue layer. When injecting fluids into each of these tissue layers, the user must exert enough force on the injection device to overcome different amounts of backpressure associated with the particular tissue layer. In general, practitioners and self-injectors, such as diabetics, are familiar with the force necessary to inject fluids into the subcutaneous layer. Injections into the subcutaneous and intramuscular tissue layers can cause discomfort to the patient or self-injector because of the characteristics of the tissue, needle length and needle diameter or gauge. It is desirable to employ shorter, smaller gauge needles to achieve delivery into the intradermal tissue layer.
It is noted that when the needle lengths are shortened and needle diameters are made smaller, the fluid dynamics of the injection device changes. Additionally, the fluid dynamics between the injection device and the targeted tissue layer also change because the shorter needle length injects the fluid into a different tissue layer, such as the intradermal layer. Because the tissue density between the intramuscular, subcutaneous, and intradermal tissue layers varies, the ease with which fluid may be injected into each type of tissue layer also varies. The variation in tissue density causes changes in the backpressure exerted by the tissue against the fluid when it is injected. For instance, the backpressure associated with the intradermal tissue layer is greater than the backpressure associated with the subcutaneous tissue layer, thereby requiring a higher pressure and/or a greater force to accomplish the injection.
Currently, several pen injection systems are commercially available for subcutaneous substance delivery of medication. These pen injection systems typically use 29 to 31 gauge needles having lengths of between 5 mm and 12.7 mm, and are used to deliver the contents of a medicament cartridge, such as insulin, to the subcutaneous tissue layers of a patient rapidly and conveniently. The medicament cartridges are generally of a standard volume and size (including a fixed cross sectional area). The pressure of delivery is the quotient of the actuation force exerted by a user and the cross sectional area of the cartridge. Because the cross-sectional area of the cartridge is fixed, higher delivery pressures require higher actuation forces by the user.
A “microneedle” pen system has been developed to facilitate subcutaneous substance delivery. Such “microneedle” drug delivery systems may include shorter needles, typically less than or equal to 3 mm, with smaller diameters, in the range of 30 to 34 gauge or thinner. Such needle length and gauge size combinations are desirable to provide for sharp, yet short, point geometries that can more accurately target substance delivery to only certain selected tissue, such as the deep intradermal or shallow subcutaneous tissue layers, thereby permitting controlled fluid delivery. Current typical pen injection systems used for subcutaneous delivery are not believed optimal for use by the general population of self-injectors for delivery into the intradermal layer because of, among other things, the high backpressures associated with injecting fluid into the intradermal layers of the skin using microneedles.
Additional details of intradermal drug delivery and microneedles have been previously described in U.S. Pat. No. 6,494,865, issued on Dec. 17, 2002, U.S. Pat. No. 6,569,143, issued on May 27, 2003, U.S. Patent Application Publication No. 2007/0185460, published Aug. 9, 2007, and U.S. Patent Application Publication No. 2005/0065472, published on Mar. 24, 2005, all of which are assigned to Becton, Dickinson and Company, and the entire content of each such patent and application being incorporated herein by reference.
The intradermal tissue layer of the skin is considerably denser than the subcutaneous tissue region. The density of the intradermal tissue layer on a particular patient is, in part, a function of his or her collagen make-up (which is affected by the patient's age) and the location of the injection site on the patient's body. This increased density of the intradermal tissue layer can create a greater backpressure resistance on the injection device than the resistance created when injecting into the subcutaneous tissue region. To overcome the increased backpressure resistance when injecting into the intradermal tissue layer with a conventional drug delivery pen, the user or patient would need to exert greater actuation force (which could be substantial) on the injector device actuator or employ some sort of powered injector device. In these applications, the injector device must be designed to withstand the greater backpressure from the intradermal injection site as well as the additional force exerted by the user or patient.
Intradermal injection of insulin and other medications provides faster uptake of the drug, thereby leading to improved therapy. Existing drug delivery devices have several limitations regarding intradermal drug delivery.
First, as noted earlier, it is inconvenient for a user to carry a vial and one or more syringes on his or her person at all times to inject medicament when required over the course of a day. Moreover, it is a tiresome process for a user to draw the desired medicament dose from the vial with a syringe needle and then inject the medicament into a tissue layer using the same syringe needle each time an injection is required.
Second, the convenience of a pen injection device is offset by the force necessary to generate sufficient pressure for an intradermal injection. The pen components can be damaged by this high force, resulting in leaking and inaccuracy at the high pressures.
There is no existing injection mechanism that takes advantage of the convenience and ease of use of a pen injection device while utilizing high pressure performance of a syringe and medicament in a vial.
Therefore, a need exists to provide an injection device that enables pen-like functionality, wherein the vial and the dosing mechanism are part of one unit and the injection is provided by a replaceable pen needle. There also exists a need for an injection device that can create high pressures for injecting viscous formulations, for injections using small gauge needles, and/or for transdermal injections. Further, there exists a need for an injection device for patient populations for which pen devices are not available or prevalent due to cost or lack of access.